Overly aggressive compression?

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darren_handler
Posts: 2
Joined: Sun Dec 10, 2017 11:10 pm

Overly aggressive compression?

Post by darren_handler » Sun Dec 10, 2017 11:20 pm

Question about the JPEG compression implemented in XnViewMP 0.88...

My 36MP camera puts out 22MB (approx) JPEG files. However, even if I make the tiniest of edits, the resulting file is now in the 3 to 4 MB range. The quality, on the surface, doesn't seem to be affected, but I haven't done any serious pixel peeping yet.

When I open up the original JPEG is Photoshop and simply do a "Save As..." I get a file of the same basic size, similar to the original. When I open the file in XNView and just do a "Save As...", the resulting size is again, seriously shrunk down into the 3 to 4 MB range, and the original is 20+ MB.

Is this something I should worry about regarding the quality of the images being saved?

Thanks in advance.

cday
XnThusiast
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Location: Cheltenham, U.K.

Re: Overly aggressive compression?

Post by cday » Mon Dec 11, 2017 7:51 am

In XnView MP compression is set in File > Format settings... , not ideal but it isn't currently possible to link from File Save as... :(

As you have noticed, images with large pixel dimensions can often be saved as JPEGs using levels of compression with little or no noticeable loss of quality, so it is up to you to decide on the trade-off depending on your needs with regard to file size and quality. You might Google for more information on that.

You might also look at File > Export... as an alternative way of compressing images.

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XnTriq
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Re: Overly aggressive compression?

Post by XnTriq » Mon Dec 11, 2017 4:30 pm

Welcome to the forum, darren_handler.

Adjusting the values for Quality (0 - 100) as well as Subsampling factor
  • 2×2,1×1,1×1 (default)
    2×1,1×1,1×1 (4:2:2)
    1×1,1×1,1×1 (best quality)
… in MP's view mode…
  • FileFormat settings...WriteJPEG
… and/or the FileExport... dialog to match the compression of your originals will minimize so-called generation loss.

If you're running on Windows, you can use JPEGsnoop to determine the “Approx quality factor” and the “Chroma subsampling” of your camera's JPEG output.

In addition to that, I recommend the following settings:
  • [   ] Progressive
    [×] Optimize Huffman table (lossless)
    DCT method [ Float (best but slowest) ]
    Smoothing factor [ 0 ]
    [×] Rebuild embedded thumbnail
    [×] Use estimated quality (when possible)
    [×] Keep EXIF
    [×] Keep IPTC
    [×] Keep XMP
    [×] Keep ICC profile

darren_handler
Posts: 2
Joined: Sun Dec 10, 2017 11:10 pm

Re: Overly aggressive compression?

Post by darren_handler » Tue Dec 12, 2017 12:03 am

Ah ha! I wasn't looking in the editor portion of the tool... I was in the overall preferences area. This should do the trick for me!

Thanks!

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